1. Field of the Invention
This invention relates to an optical recording medium for optically recording and reproducing various information signals such as image information, etc., and more particularly to an optical recording medium on which an information is recorded at a high density. Also, the present invention is directed to a method and apparatus of reproducing an information recorded on the high-density recording medium.
2. Description of the Related Art
Recently, an optical recording medium and an electromagnetic recording medium and so forth has been commercially available as an information recording medium for recording various information such as audio and video information, etc. In the optical recording medium, there have been propagated or developed a read-only type disc such as CD-ROM and DVD-ROM including a existent CD (compact disc), a WROM (write once read many) type disc such as CD-R (recordable) and DVD-R, etc., and a rewritable disc such as CD-RW (rewritable) and DVD-RAM, etc.
In such an optical recording medium, the read-only type disc has the structure consisting of a transparent substrates which is usually made from polycarbonate, etc. and has an information recorded on one face thereof, a reflective film which is deposited on the information recording face of the transparent substrate and is made from an aluminum material with a high reflectivity, and a protective layer which is formed on the reflective film and is made from a plastic material, etc. On the information recording face of the transparent substrate an information is recorded in a form of recording mark, for example, pit train with a concave and convex shape. In other words, as shown in FIG. 1, an optical recording medium 10 stores an information in a pit train shape 12 which makes a track extended from-the inner circumference into the outer circumference in a spiral or concentric circle shape.
An information recorded on the optical recording medium in this manner is reproduced by means of an optical pickup for irradiating a light beam onto a track to be reproduced through the transparent substrate and detecting a reflective light amount. In this case, a reflective light reflected from a mirror 12B between pits 21A is detected into xe2x80x9cbrightnessxe2x80x9d while a reflective light reflected from the pit 12A is detected into xe2x80x9cdarknessxe2x80x9d. This is caused by a fact that a light beam irradiated onto the mirror 12B transmits the mirror 12B and is full-reflected by the reflective film while a light beam irradiated onto the pit 12A is diffused-reflected by the pit 12A to reduce a reflectivity. The reflective light beam detected into xe2x80x9cbrightnessxe2x80x9d or xe2x80x9cdarknessxe2x80x9d is converted into a shape of electrical signal by means of a photo detector and then is signal-processed such that it is reproduced into an information in a shape of channel bit stream. This reproduction mechanism has been similarly applied to a phase change opto-magnetic recording system besides a recording method according to the pit train 12.
Referring to FIG. 2, there is shown a procedure of a recording and reproducing method for the conventional optical recording medium. When an information is recorded on the recording medium, in step 1, a user data to be recorded is added with an error correction code (ECC) for a predetermined block unit and divided into a sector unit, whereby it is converted into a shape of data channel. In step 2, the data channel is modulated and is added with a synchronizing signal in the frame unit to thereby be converted into a shape of channel bit stream (CBS) . Then, in step 3, the channel bit stream is light-modulated and applied to the light source of the optical pickup. In step 4, the light source irradiates a recorded light beam according to a recorded data light-modulated and inputted to record an information in a shape of pit train 12 as shown in FIG. 3. The above-mentioned recording process is similarly applied to a disc fabrication process employing an exposure device in the case of a recordable optical recording medium as well as a read-only type optical recording medium (i.e., ROM type disc).
On the other hand, when an information recorded on the optical recording medium shown in FIG. 3 is reproduced, in step 5, a reproduced light beam from the light source is irradiated to trace a track defined by the pit train of the optical recording medium 10. As shown in FIG. 3, A light amount reflected from the optical recording medium 10 is detected and converted into an electrical signal to thereby detect a reproduced signal, that is, a radio frequency (RF) signal. In this case, the radio frequency signal RF has a low level at the pit 12A while having a high level at the mirror 12B. In step 6, such a radio frequency signal is equalized and sliced such that it is converted into a shape of channel bit stream CBS as shown in FIG. 3. The channel bit stream CBS is demodulated into a data channel shape in step 7 and processes an error correction code included in the data channel in step 8, thereby reproducing a user data recorded on the optical recording medium.
In an optical recording medium having such a recording and reproducing mechanism, there has been attempted various schemes for enhancing a recording density in accordance with an increased requirement intended to record a high capacity of information such as a moving picture, etc. More specifically, in the case of a CD and a DVD, there has been attempted a scheme of reducing a recording mark or a size of pit, or reducing a track pitch so as to enhance a recording density. To this end, there has been developed techniques of making use of a short wavelength of light source to enlarge the number of aperture of the objective lens and reduce a spot size of light beam. However, since reducing a spot size of light beam has a limit ultimately, reducing a pit size and a track space must be limited.
For example, a read-only type optical recording medium is fabricated by preparing an circular plate of a disc defined with a desired pit using an exposure device and making a inversive transcription of the pit formed in the circular plate to prepare a stamper, and thereafter by duplicating the disc, that is, molding a disc substrate using the stamper. In recent, it becomes possible to form minute pit in accordance with a development of argon (Ar) laser, etc. In a reproducing apparatus, however, there has not yet been a light source corresponding to the minute pit. As a result, since a pit size and a track pitch should be limited within a range that can be read by the reproducing apparatus, it has a limit to enlarge a capacity of the read-only type optical recording medium.
Accordingly, it is an object of the present invention to provide an optical recording medium that is capable of enlarging a recording density.
Further object of the present invention is to provide an optical recording medium that can enhance a recording density and have a changeablity with the existent recording media such as CD, DVD and so forth.
Still further object of the present invention is to provide an optical reproducing method and apparatus for reproducing an information recorded on the above-mentioned optical recording medium.
Still further object of the present invention is to provide an optical reproducing method and apparatus that can reproduce an information recorded at a high density using a relatively long wavelength of light source.
Still further object of the present invention is to provide an optical reproducing method and apparatus that can reproduce an information recorded on tracks by a long wavelength of light source when the tracks have been formed in correspondence with a short wavelength of light source.
In order to achieve these and other objects of the invention, an optical recording medium according to one aspect of the present invention includes a substrate; and an information recording face having an information recorded as pit trains and consisting of a track having any one of a concentric circle and spiral shape, wherein at least two pit trains are arranged adjacently in such a manner to be reproduced by a single light beam.
An optical reproducing method according to another aspect of the present invention includes the steps of irradiating a single light beam onto at least two tracks with respect to an optical recording medium having a track in which an information is recorded as pit trains; detecting and converting a reflective light from the optical recording medium using a photo detector divided into a plurality number, and combining the converted light detecting signals to thereby detect a plurality of radio frequency signals; and processing the plurality of radio frequency signals to detect information corresponding to each of said at least two tracks.
An optical reproducing apparatus according to still another aspect of the present invention includes light beam generating means for irradiating a single light beam onto at least two tracks with respect to an optical recording medium having a track in which an information is recorded as pit trains; signal detecting means for dividing a light reflected from the optical recording medium into a plurality number and detecting and converting the same, and combining the converted light detecting signals to thereby detect a plurality of radio frequency signals; and means for processing the plurality of radio frequency signals to detect information corresponding to each of said at least two tracks.